Various studies have been conducted on how different ambient lights (artificial and natural lights) affect humans differently. This effect, often called the Kruithof effect, indicates the psychological effect that ambient light has on humans. As shown in the graph of FIG. 6, light with a low color temperature is not pleasing to humans at high intensities, but is pleasing at low intensities. On the other hand, light with a high color temperature is not pleasing to humans at low intensities, but is pleasing at high intensities. Thus, the range of light intensities considered to provide pleasing illumination differs according to the color temperature of the ambient light. In FIG. 6, “A” indicates an incandescent lighting, “B” indicates a fluorescent lighting (warm white), “C” indicates a fluorescent lighting (white), “D” indicates a fluorescent lighting (cool white), and “E” indicates a fluorescent lighting (daylight).
Some conventional lighting fixtures have accounted for this Kruithof effect. For example, one such lighting fixture can emit light in a plurality of white colors, such as daylight, cool white, white, warm white, and extra warm white through a combination of blue LEDs having a high color temperature and yellow LEDs having a low color temperature. The lighting fixture produces the different white colors by adjusting the light intensity produced by the blue LEDs while keeping the intensity of the yellow LEDs fixed. Hence, the light intensity of the lighting fixture increases when the intensity of the blue LEDs increases (i.e., when the color temperature rises).